In the processing of integrated circuit (IC) devices, yield is a key economical parameter that IC manufacturers pay close attention to. Poor yielding devices impact manufacturing cycle time, resource allocation, on-time delivery, market share, and profits among other things. Excessive or high leakage current is often one parameter that causes poor yields in IC manufacturing. High leakage current is typically caused by the presence of fast diffusing impurities or defects in active device regions within a semiconductor substrate.
One known method of reducing this problem is referred to as extrinsic gettering, which is a process to remove the unwanted impurities from critical regions of IC devices and prevent formation of impurity related defects. In a typical extrinsic gettering process, a single polycrystalline semiconductor layer is deposited on the back or lower surface (i.e., the surface opposite the surface where active devices are formed) of a monocrystalline semiconductor substrate prior to any high temperature process. The presence of the polycrystalline layer induces stress on the semiconductor substrate, which acts to getter or remove the unwanted impurities during subsequent high temperature processing and prevent formation of impurity related defects. Unfortunately, during the subsequent high temperature process steps the polycrystalline silicon layer itself recrystallizes, and thus loses a significant part of its gettering capability.
Accordingly, an improved gettering structure and method are needed that address the issues associated with prior art gettering techniques including those set forth above.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description.